SmartDefiApp is a smart contract designed to simplify and unify core DeFi operations such as token swaps and liquidity management, using a Uniswap V2-compatible router. It enables users to swap between ERC-20 tokens and ETH, provide liquidity using either one or two tokens, and remove liquidity with full control over slippage and deadlines — all from a single, streamlined interface.
The contract supports major stablecoins like USDC, USDT, and DAI by default, making it well-suited for real-world use cases and integrations with other protocols. Its logic handles the complexities of token approvals, routing, and safe transfers under the hood, so developers can focus on building user-facing applications without reinventing swap or liquidity flows.
Built in Solidity 0.8.28, SmartDefiApp leverages OpenZeppelin’s SafeERC20 for secure token handling and is fully tested on Arbitrum One using the Foundry framework. It’s a modular, gas-efficient base for any dApp, aggregator, or DeFi tool aiming to interact with liquidity pools in a reliable and extensible way.
| Feature | Description |
|---|---|
| 🔄 Token ↔ Token Swaps | Swap ERC-20 tokens via customizable paths. |
| 🌐 ETH ↔ Token Swaps | Seamlessly convert between ETH and tokens. |
| 💧 Liquidity Management | Add/remove liquidity using one or two tokens. |
| 🛡️ Secure Transfers | Utilizes SafeERC20 from OpenZeppelin for secure operations. |
| 🧪 Foundry Test Suite | Comprehensive test coverage using real tokens and addresses. |
| 📡 Event Logging | Emits events for every operation, including liquidity removal. |
The SmartDefiApp protocol is composed of a single smart contract designed to simplify and standardize token swaps and liquidity interactions on EVM-compatible blockchains. Below is a breakdown of the components and their responsibilities:
| Contract | Description |
|---|---|
SmartDefiApp |
Core contract of the protocol. Handles token swaps (ERC-20 and ETH), single- and dual-token liquidity provisioning, and liquidity removal. Uses a Uniswap V2-compatible router under the hood. |
IRouterV2 |
Interface used to interact with external routers such as Uniswap V2 or SushiSwap. Supports swapping, adding, and removing liquidity. |
IFactory |
Interface for querying LP token pair addresses from a Uniswap V2-compatible factory. Used during liquidity operations. |
- Router: Arbitrum RouterV2 – used for executing swaps and managing liquidity
- Factory: Arbitrum Factory – used to locate LP token addresses
- Tokens: Supports USDC, USDT, DAI, and WETH on Arbitrum One
- OpenZeppelin Contracts: OpenZeppelin Contracts
- Foundry: Foundry
constructor(address RouterV2Address_, address FactoryAddress_, address USDT_, address USDC_, address DAI_)Initializes the contract with the router and factory addresses, and the supported stablecoins (USDT, USDC, DAI).
| Function | Description |
|---|---|
swapExactTokensForTokens |
Swaps a fixed amount of tokens for a minimum output. |
swapTokensForExactTokens |
Swaps tokens to receive a fixed output. |
swapExactETHForTokens |
Swaps a fixed amount of ETH for tokens. |
swapTokensForExactETH |
Swaps tokens to receive a fixed amount of ETH. |
swapExactTokensForETH |
Swaps a fixed amount of tokens for ETH. |
addLiquidityFromOneToken |
Adds liquidity using a single token (splitting and swapping). |
addLiquidityFromTwoTokens |
Adds liquidity using both tokens directly. |
removeLiquidity |
Removes liquidity and returns token balances. |
| Event | Description |
|---|---|
SwapERC20Tokens |
Emitted on token-to-token swap. |
SwapETHForTokens |
Emitted on ETH-to-token swap. |
SwapTokensForETH |
Emitted on token-to-ETH swap. |
AddLiquidity |
Emitted after liquidity is added. |
RemoveLiquidity |
Emitted after liquidity is removed. |
| Modifier | Description |
|---|---|
validPairs |
Ensures the pair is composed of valid stablecoins. |
This section explains how to interact with the SmartDefiApp smart contract deployed on the Arbitrum One network. It covers how to perform token swaps, add and remove liquidity, and provides a real transaction example to follow.
🔗 Deployed Contract: 0xcc0029c0109b12b108f1c3bce5bdc1dcec6ced9c on Arbiscan
To swap one token for another using SmartDefiApp:
- Go to the Write Contract tab on Arbiscan and connect your wallet (make sure it's on Arbitrum One).
- Approve the contract to spend your token using the token’s own contract (via
approve(spender, amount)). - Call
swapExactTokensForTokenswith:amountIn_: amount of tokens to swap (e.g.1500000for 1.5 USDC)amountOutMin_: minimum amount of output tokens acceptedpath_: array of token addresses (e.g.[USDC, USDT])to_: your wallet addressdeadline_: Unix timestamp (e.g.block.timestamp + 600)
✅ Example: Swap 1.5 USDC → USDT
amountIn_:1500000amountOutMin_:1400000path_:[0xaf88d065e77c8cC2239327C5EDb3A432268e5831, 0xFd086bC7CD5C481DCC9C85ebE478A1C0b69FCbb9]to_: your wallet addressdeadline_: current time + 10 minutes
To provide liquidity to a token pair (e.g. USDT/DAI):
- Approve the contract to spend both tokens.
- Use
addLiquidityFromTwoTokenswith:amountA_andamountB_: amounts of each tokentokenA_andtokenB_: token addressesamountAMin_andamountBMin_: slippage tolerancesdeadline_: timestamp deadline
You can also use addLiquidityFromOneToken to deposit one token and have the contract split and convert it to form a pair automatically.
To remove liquidity and receive your underlying tokens:
- Use
removeLiquiditywith:tokenA_andtokenB_: the token pairliquidity_: amount of LP tokens to withdrawamountAMin_,amountBMin_: minimum tokens to receiveto_: your addressdeadline_: timestamp
Make sure you've approved the contract to spend your LP tokens.
Here is a real transaction on Arbitrum using this contract to swap tokens:
🔹 Tx Hash: 0x392aaee3eeb91cf43de2b3df107bde1d8893d4210adc63f490e192adf9f91d0c
- Swapped: 0.0005 WETH → 1.23 USDT
- Path:
[WETH, USDT] - User:
0x... - Contract:
SmartDefiApp
You can interact with the contract directly via Arbiscan or through a front-end interface that supports contract method encoding and Web3 wallet interaction (e.g. Etherscan, Remix, or your custom dApp).
All swap and liquidity functions are thoroughly tested with Foundry using real user addresses and tokens on the Arbitrum One mainnet.
| Test | Description |
|---|---|
testInitialDeploy |
Validates contract initialization. |
testSwapExactTokensForTokens |
Token-to-token swap with fixed input. |
testSwapTokensForExactTokens |
Token-to-token swap with fixed output. |
testSwapExactTokensForETH |
Token-to-ETH swap with fixed input. |
testSwapTokensForExactETH |
Token-to-ETH swap with fixed output. |
testSwapExactETHForTokens |
ETH-to-token swap with fixed input. |
testAddLiquidityFromOneToken |
Liquidity addition using one token. |
testAddLiquidityFromTwoTokens |
Liquidity addition using two tokens. |
testRemoveLiquidity |
Tests removal of liquidity. |
testIncorrectSwapExactETHForTokens |
Ensures function reverts with 0 ETH input. |
testIncorrectPairAddLiquidity* |
Ensures validation of token pair constraints. |
testIncorrectAmountAddLiquidity* |
Ensures non-zero amount validation. |
forge test| File | % Lines | % Statements | % Branches | % Functions |
|---|---|---|---|---|
src/SmartDefiApp.sol |
100.00% (67/67) | 100.00% (62/62) | 100.00% (10/10) | 100.00% (11/11) |
This project is licensed under the MIT License.